diff --git a/oni-csharp/oni-csharp.el b/oni-csharp/oni-csharp.el
index 11c1dcf..02b1cd7 100644
--- a/oni-csharp/oni-csharp.el
+++ b/oni-csharp/oni-csharp.el
@@ -4,7 +4,7 @@
 
 ;; Author: Tom Willemse <tom@ryuslash.org>
 ;; Keywords: local
-;; Version: 2022.0105.161232
+;; Version: 2022.0202.115001
 ;; Package-Requires: (csharp-mode oni-company oni-flycheck oni-yasnippet oni-hydra oni-lsp oni-smartparens)
 
 ;; This program is free software; you can redistribute it and/or modify
@@ -78,54 +78,6 @@ _cs_: Solution
   (let ((compile-command (concat oni-csharp-devenv-executable " /Build Debug " (oni-csharp-locate-dominating-file-wildcard "*.sln") " /project " (oni-csharp-locate-dominating-file-wildcard "*.csproj"))))
     (compile compile-command)))
 
-(defun oni-csharp-collect-project-names ()
-  "Go through the current buffer and collect all the project names."
-  (interactive)
-  (clrhash oni-csharp--projects)
-  (save-excursion
-    (goto-char (point-min))
-    (while (re-search-forward
-            (rx bol
-                "Project(\"{"
-                (group (minimal-match (1+ (or alphanumeric "-"))))
-                "}\") = \""
-                (group (minimal-match (1+ any)))
-                "\", \""
-                (minimal-match (1+ any))
-                "\", \"{"
-                (group (minimal-match (1+ any)))
-                "}\""
-                eol)
-            nil
-            :noerror)
-      (puthash (match-string-no-properties 3)
-               (match-string-no-properties 2)
-               oni-csharp--projects))))
-
-(defun oni-csharp-display-project-names ()
-  "Display the project names in the current buffer."
-  (interactive)
-  (save-excursion
-    (goto-char (point-min))
-    (remove-overlays (point-min) (point-max) 'oni-csharp--overlayp t)
-    (while (re-search-forward
-            (rx bol
-                (zero-or-more whitespace)
-                "{"
-                (group (minimal-match (one-or-more (or alphanumeric "-"))))
-                "} = {"
-                (group (minimal-match (one-or-more (or alphanumeric "-"))))
-                "}"
-                eol)
-            nil
-            :noerror)
-      (let ((current-overlay (make-overlay (line-beginning-position) (line-end-position))))
-        (overlay-put current-overlay 'after-string
-                     (propertize (format "  => %s" (gethash (match-string 1) oni-csharp--projects))
-                                 'face '(:foreground "#808080")))
-        (overlay-put current-overlay 'oni-csharp--overlayp t)
-        (overlay-put current-overlay 'evaporate t)))))
-
 (defun oni-csharp--auto-fill-mode ()
   "Enable ‘auto-fill-mode’ only for comments."
   (setq-local comment-auto-fill-only-comments t)
@@ -203,5 +155,63 @@ _cs_: Solution
   (with-eval-after-load 'yasnippet
     (oni-csharp-snippets-initialize)))
 
+;;; Solution mode
+
+(defun oni-csharp-collect-project-names ()
+  "Go through the current buffer and collect all the project names."
+  (interactive)
+  (clrhash oni-csharp--projects)
+  (save-excursion
+    (goto-char (point-min))
+    (while (re-search-forward
+            (rx bol
+                "Project(\"{"
+                (group (minimal-match (1+ (or alphanumeric "-"))))
+                "}\") = \""
+                (group (minimal-match (1+ any)))
+                "\", \""
+                (minimal-match (1+ any))
+                "\", \"{"
+                (group (minimal-match (1+ any)))
+                "}\""
+                eol)
+            nil
+            :noerror)
+      (puthash (match-string-no-properties 3)
+               (match-string-no-properties 2)
+               oni-csharp--projects))))
+
+(defun oni-csharp-display-project-names ()
+  "Display the project names in the current buffer."
+  (interactive)
+  (save-excursion
+    (goto-char (point-min))
+    (remove-overlays (point-min) (point-max) 'oni-csharp--overlayp t)
+    (while (re-search-forward
+            (rx bol
+                (zero-or-more whitespace)
+                "{"
+                (group (minimal-match (one-or-more (or alphanumeric "-"))))
+                "} = {"
+                (group (minimal-match (one-or-more (or alphanumeric "-"))))
+                "}"
+                eol)
+            nil
+            :noerror)
+      (let ((current-overlay (make-overlay (line-beginning-position) (line-end-position))))
+        (overlay-put current-overlay 'after-string
+                     (propertize (format "  => %s" (gethash (match-string 1) oni-csharp--projects))
+                                 'face '(:foreground "#808080")))
+        (overlay-put current-overlay 'oni-csharp--overlayp t)
+        (overlay-put current-overlay 'evaporate t)))))
+
+(define-derived-mode csharp-solution-mode prog-mode "Sln"
+  "A major mode for viewing and editing C# ‘.sln’ files."
+  (oni-csharp-collect-project-names)
+  (oni-csharp-display-project-names))
+
+;;;###autoload
+(add-to-list 'auto-mode-alist `(,(rx ".sln" eos) . csharp-solution-mode))
+
 (provide 'oni-csharp)
 ;;; oni-csharp.el ends here